RDMA/siw: Relax from kmap_atomic() use in TX path

Since the transmit path is never executed in an atomic context, we do not
need kmap_atomic() and can always use less demanding kmap().

Link: https://lore.kernel.org/r/20190909132945.30462-1-bmt@zurich.ibm.com


Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>